High-strength low alloy ferritic steel small-gauge wire

ABSTRACT

THE PROCESS FOR PRODUCING HIGH-STRENGTH FERRITIC STEEL SMALL-GAUGE WIRE HAVING A DIAMETER UP TO 1 MILLIMETER COMPRISING REDUCING THE DIAMETER OF A KILLED LOW ALLOY STEEL ROLLED STARTING WIRE, SAID STEEL CONTAINING BETWEEN ABOUT 0.01 AND 0.06 CARBON, BETWEEN ABOUT 0.05 AND 1% SILICON, BETWEEN ABOUT 0.25 ND 6% MANGANESE, BETWEEN ABOUT 0.01 AND 0.30% NIOBIUM, UP TO 0.03% NITROGEN, UP TO 0.2% ALUMINUM, UP TO 0.5% ZICRTONIUM, UP TO 0.30% VANADIUM, AND UP TO 0.5% TITANIUM, BY SEQUENTIAL PASSES THROUGH DRAWING DIES CONSTITUTING A DRAWING CYCLE, FOLLOWED BY TEMPERING AT A TEMPERATURE BETWEEN ABOUT 400*C. AND 670*C., AND FURTHER REDUCTIION WITH AT LEAST ONE ADDITIONAL DRAWING CYCLE, WITH TEMPERING AT A TEMPERATURE BETWEEN ABOUT 400*C AND 670*C. BETWEEN EACH SAID DRAWING CYCLE, UNTIL THE PRODUCT WIRE DIMENSION IS OBTAINED. THE INVENTION ALSO INCLUDES THE TOUGH HIGH-STRENGTH KILLED LOW ALLOY FERRITIC STEEL WIRE PRODUCE BY SAID PROCESS.

United States Patent 3,674,570 HIGH-STRENGTH LOW ALLOY FERRITIC STEEL SMALL-GAUGE WIRE Ingemar Gustaf Terje Hallstrom, Martin Holger Jarleborg, and Stig-Goran Harry Tarnblom, Fagersta, Sweden, assignors to Fagersta Bruks AB, Fagersta, Sweden N0 Drawing. Filed Jan. 21, 1071, Ser. No. 108,592 Claims priority, application Sweden, Feb. 11, 1970, 1,272/ 70 Int. Cl. (321d 9/52 U.S. Cl. 148-12 9 Claims ABSTRACT OF THE DISCLOSURE The process for producing high-strength ferritic steel small-gauge wire having a diameter up to 1 millimeter comprising reducing the diameter of a killed low alloy steel rolled starting wire, said steel containing between about 0.01 and 0.06 carbon, between about 0.05 and 1% silicon, between about 0.25 and 6% manganese, between about 0.01 and 0.30% niobium, up to 0.03% nitrogen, up to 0.2% aluminum, up to 0.5 zirconium, up to 0.30% vanadium, and up to 0.5% titanium, by sequential passes through drawing dies constituting a drawing cycle, followed by tempering at a temperature between about 400 C. and 670 C., and further reduction with at least one additional drawing cycle, with tempering at a temperature between about 400 C. and 670 C. between each said drawing cycle, until the product wire dimension is obtained. The invention also includes the tough high-strength killed low alloy ferritic steel wire produced by said process.

BACKGROUND OF THE INVENTION High-strength small-gauge wire, for example, tire reinforcing wire, is generally produced from a carbon steel containing 0.70% C., 0.20% Si and 0.60% manganese. The wire drawing process for the production of the aforesaid high-strength high carbon wire involves a continuous heat treatment requiring two stages before each cycle of wire drawing. The foregoing treatment, which is also performed on the rolled starting wire, is called patenting. The wire is austenitized over the A point between 900950 C. and is then immediately converted at a temperature of approximately 500 C. A continuous conveyor furnace with air or combustion gas atmosphere is usually utilized for the austenitizing. The conversion is usually in a bath furnace, usually with a molten lead bath. After patenting, the wire surface is normally oxidized and this oxide must be removed prior to the next wire drawing step. The oxide is usually removed by pickling in sulfuric or hydrochloric acid. The wire is then drawn with maximum reduction per drawing down to a dimensions somewhat larger than the dimension where material brittleness occurs. The wire is then again patented and cycles of patenting/drawing repeated until the desired wire product dimension is obtained.

WVhen producing high-strength small-gauge wire of carbon steel, it is very important that the material have a low content of impurities, particularly such impurities as phosphorus, sulfur and oxygen. Slag and other inclusions in the Wire substantially increase the risk of wire breakage. This is due to the inclusions acting as notches. The pearlite structural constituent of this type of steel is sensitive to notches. Because of the high temperature of the austenitizing treatment, patenting involves considerable risk of oxidation and decarburization of the wire surface. Sanitary (health, cleanliness and safety) problems exist because of the conversion process (at 500 "ice C.) being generally carried out in a lead bath. The acid pickling bath involves similar inconveniences.

It is an object of the present invention to produce in a simpler, cleaner and more efiicient manner high-strength small-gauge wire for uses such as ropes, and reinforcing wire. It is also an object of the present invention to provide high-strength, low carbon ferritic steel smallgauge wire.

SUMMARY OF THE INVENTION The present invention provides a process for producing high-strength steel small-gauge wire having a diameter up to 1 millimeter comprising reducing the diameter of a killed low alloy steel rolled starting wire, said steel containing between about 0.01 and 0.06% carbon, between about 0.05 and 1% silicon, between about 0.25 and 6% manganese, between about 0.01 and 0.30% niobium, up to 0.03% nitrogen, up to 0.2% aluminum, up to 0.5 zirconium, up to 0.30% vanadium, and up to 0.5% titanium, by sequential passes through drawing dies constituting a drawing cycle, followed by tempering at a temperature between about 400 C. and 670 C., and further reduction with at least one additional drawing cycle, with tempering at a temperature between about 400 C. and 670 C. between each drawing cycle, until the product wire dimension is obtained.

The present invention further provides a tough highstrength killed low alloy ferritic steel small-gauge wire having a diameter up to 1 millimeter, said steel wire consisting essentially of between about 0.01 and 0.06% carbon, between about 0.05 and 1% silicon, between about 0.25 and 6% manganese, between about 0.01 and 0.30% niobium, up to 0.03% nitrogen, up to 0.2% aluminum, up to 0.5 zirconium, up to 0.30% vanadium, and up to 0.5 titanium, said steel wire having a resistance to rupture of up to about 275 kg./n1m. and an elongation of at least about 2% on a measured length of 200 millimeters.

DETAILED DESCRIPTION OF THE INVENTION The heat treatment between successive drawing cycles consists of tempering within the temperature range of about 400-670 C. Said heat treatment may be carried out more simply and using less expensive heat treatment equipment than in the patenting process. Continuous heat treatment is most suitable, e.g., high frequency heating or direct resistance heating. These two methods used in combination with the drawing eliminate the treating time of two separate heat treatments and certain of the costs incident thereto. The heat treatment can also although it is less attractive be carried out in soaking pits bath-furnaces or bell-type furnaces. Protective atmosphere equipment can readily be used in conjunction with high frequency heating or with direct resistance heating, thereby substantially avoiding oxidation and minimizing the possible use of pickling and often making pickling unnecessary.

The protective atmosphere may be a conventional nonoxidizing atmosphere of the type used in heat treating steel at the temperatures specified.

The wire product having the aforesaid composition is ferritic. It is substantially free of pearlite. As a result, the notch effect resultant from inclusions is considerably lower than that of conventional carbon steel wire. Because of the steel wires aforesaid structure, the steel exhibits a slow rate of strain hardening during working with the consequence that it is possible to perform large reductions per drawing and a large total reduction during a drawing cycle. The term drawing cycle is used to designate sequential drawings of the wire without intermediate heat treatment. Heat treatment is effected between successive drawing cycles. As a result of the low carbon content of the wire, there is no risk of'decarburization during processing. On the contrary, carburization must be avoided. Carburization is avoided more simply than the procedures requisite to avoid decarburization.

The process of the present invention has the additional advantage that it is not necessary to heat treat the rolled starting wire before the firstd rawing cycle.

The invention is further illustrated in the following example in which rolled wire stock (referred to herein as starting wire) having an initial diameter of 5.6 millimeters (mm.) is drawn to small-gauge wire having a diameter of 0.15 mm. The initial rolled steel wire had an analysis of 0.03% C., 0.25% Si, 3.5% Mn, 0.10% Nb, and 0.010% N. The first drawing cycle with 30-35% re- "duction per drawing (by passing through a drawing die) reduced the initial rolled Wire to a diameter of 1.50 mm. It was then tempered. Th drawing cycle utilized reductions of approximately -25% per drawing. The second drawing cycle reduced the diameter to 0.43 mm., with the third drawing cycle reducing the diameter to the finished diameter of 0.15 mm. Tempering between first and second drawing cycles at a temperature of about 600 'C. and tempering between second third drawing cycles was at a temperature of about 4500 C. The product highstrength ferritic steel wire having a diameter of 0.15 mm. had a resistance to rupture (tensile strength)'-of 265-275 kg./mm. and anelongation of 2% on a measured length of 200 mm. A test of the toughness by means of the socalled loop test was satisfactory. In the said loop test, the wire is looped and the loop is contracted to a tie which must not cause breakage of the wire until a certain specified age.

Similar high-strength tough wire as for the exemplified wire is produced from the other steel compositions within the ranges specified. Such wire is particularly useful for producing a wire rope, and wire reinforcement for a variety of industrial products, e.e., tires and hoses.

' In addition to the advantages of the invention described hereinbefore, the process advantages include the absence of the lead bath with the consequent health, cleanliness and safety problems. The low temperature heat treatment utilized, together with hte low carbon content of the wire, results in little if any decarburization. Additionally, the surface oxidation during heat treatment is slight, implying a lower acid consumption even should pickling be necessary.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of gen, up to 0.2% aluminum, up to 0.5% zirconium, up to 0.30% vanadium, and up to 0.5% titanium, by sequential '4 1 i passes through drawing dies constituting a drawing cycle, followed by tempering at a temperature between about 400 C. and 670 C., and further reduction with at least one additional drawing cycle, with tempering at a temperature between about 400 C. and 670 C. between each said drawing cycle, until the product wire dimensionis obtained.

2. The process of claim 1 wherein said wire is pickled after tempering.

3. The process of claim 1 wherein said Wire is tempered utilizing high frequency heating to attain said tempering temperature.

4. The process of claim 1 wherein said wire is tempered utilizing direct resistance heating to attain said tempering temperature. i i i 5. The process of claim 1 wherein said tempering is carried out in a non-oxidizing atmosphere.

6. The process for producing high-strength steel smallgauge wire having a diameter up to 1 millimeter, said steel wire being a killed low alloy steel consisting essentially of between about 0.01 and 0.06% carbon, between about 0.05 and 1% silicon, between about 0.25 and 0.75% manganese, between about 0.01 and 0.30% niobium, up to 0.03% nitrogen, up to 02% aluminum, up to 0.5% zirconium, up to 0.3% vanadium, and up to 0.5% titanium, comprising reducing a rolled starting wire to the final dimension in one drawing cycle without any heat treatment.

7. A tough high-strength killed low alloy ferritic steel small-gauge wire having a diameter up to 1 millimeter, said steel wire consisting essentially of between about 0.01 and 0.06% carbon, between about 0.05 and 1% silicon, between about 0.25 and 6% manganese, between about 0.01 and 0.30% niobium, up to 0.03% nitrogen, up to 0.2% aluminum, up to 0.5% Zirconium, up to 0.30% vanadium, and up to 0.5 titanium, said steel wire having a resistance to rupture of up to about 275 kg./mm. and an elongation of at least about 2% on a measured length of 200 millimeters.

8. The tough high-strength small-gauge wire of claim 7 consisting essentially of 0.03% carbon, 0.25% silicon,

3.5% manganese, 0.10% niobium, and 0.010% nitrogen.

9. The tough high-strength small-gauge wire of claim 7 having a manganese content of between about 0.25 and 0.75%.

OTHER REFERENCES Controlled-Cooled Structural Steels Modified with Cb, Mo, and B, Trans. of the ASM, Cryderman et al., vol. 62, 1969, pp. 561-574.

L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 148l2.l, 12.3, 36 

